Notes

3. May lose their crystalline structure due to radiation (metamictization).

4. In modern times, hyacinth or jacinth usually refers to reddish brown zircon, which belongs to the tetragonal crystal system. However, historically it has also been used to refer to hessonite (cubic), topazes (orthorhombic), and various other gemstones.

5. Mimetite has also been classed as a monoclinic, pseudo-hexagonal crystal.

6. Both natural and synthetic stones. (Natural moissanite crystals are too small to cut).

8. Many of the materials mineralogists have classed as trigonal crystals have been classed by gemologists as hexagonal crystals in a trigonal subclass. Thus, you’ll find many of the gems listed here classed as hexagonal in their individual gem listings.